The present invention relates to a screen printing apparatus and a screen printing method for printing a paste such as cream solder onto a substrate.
For soldering an electronic component, there is known a method utilizing a solder bump or a solder precoating. In such method, a solder bump which is a protruding solder electrode or a solder precoat which is a solder film is formed for soldering, on an electrode of a work such as an electronic component or a substrate. In such solder forming step, a screen printing is widely employed as a method of solder supply. In such printing method, cream solder is printing on an upper surface of the work, through a hole pattern provided in a mask plate. In the screen printing operation, after a squeezing step of moving a squeezee, there is executing a mask separating step of separating the substrate from the lower surface of the mask plate. In such mask separating operation, the substrate is lowered by clamp members which clamp the substrate from both sides thereof at a printing position, in a state supporting the lower surface of the mask plate, whereby the substrate is separated from the mask plate (for example cf. Patent Literature 1).
Patent Literature 1:JP-A-7-214748
Recently, the electronic components are becoming finer to result in a smaller pitch of the electrodes formed on the work, whereby a large number of electrodes are arranged at a high density. Therefore, the mask plate employed for forming bumps on such electrodes have a thickness significantly smaller than that in a related mask plate employed for solder printing on a printed circuit board. However, such mask plate of a smaller thickness designed for the work having electrodes of such high density, in case applied to a related screen printing method, causes following drawbacks.
In order to attain a satisfactory printing quality in the screen printing, there are required a filling property of securely filling cream solder in the hole pattern and a satisfactory mask separating property, at a mask plate separation from the work after such filling, that the cream solder can be separated without a profile destruction from the pattern hole. However, the printing operation is becoming more difficult with the increasing density of the electrodes and the thinner mask and it is particularly difficult to ensure a satisfactory mask separating property over the entire area of the work.